The present invention relates generally to resonant converters, and more particularly, to a resonant converter having an actively-controlled resonant preload.
It is generally well known that conventional series resonant converters cannot be operated effectively at no load or minimal load. In an attempt to eliminate this problem, a third element is added to the conventional series resonant converter. A paper entitled "Topologies for Three Element Resonant Converters", by Rudy Sevems, published in APEC, 1990, page 712, references substantially all known resonant converter designs incorporating reactive third elements. This paper discusses two element resonant topologies, and describes how many of the limitations of the two element designs can be overcome by adding the third reactive element.
A paper entitled "A Comparison of Half-Bridge resonant Converter Topologies, by Robert L. Steigerwald" published in IEEE Transactions on Power Electronics, Vol. 3, No. 2, April 1988, discusses half-bridge series resonant, parallel resonant and combination series-parallel resonant converters. This paper indicates that the combination series-parallel converter, which takes on the desirable characteristics of the pure series and the pure parallel converter, and thus removes the main disadvantages of these two converters. It is shown that the combination series-parallel converter can run over a large input voltage range and a large load range (no load to full load) while maintaining excellent efficiency.
Accordingly, it is an objective of the present invention to provide for a resonant converter that is able to effectively regulate from no load to full load.